Fluid ejection devices in inkjet printers provide drop-on-demand ejection of fluid drops. Inkjet printers print images by ejecting ink drops through a plurality of nozzles onto a print medium, such as a sheet of paper. The nozzles are typically arranged in one or more arrays, such that properly sequenced ejection of ink drops from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium move relative to each other. In a specific example, a thermal inkjet printhead ejects drops from a nozzle by passing electrical current through a heating element to generate heat and vaporize a small portion of the fluid within a firing chamber. In another example, a piezoelectric inkjet printhead uses a piezoelectric material actuator to generate pressure pulses that force ink drops out of a nozzle.
Although inkjet printers provide high print quality at reasonable cost, continued improvement relies on overcoming various challenges that remain in their development. One challenge, for example, is managing air bubbles that develop in inkjet printheads. The presence of air bubbles in channels that carry ink to printhead nozzles often results in faulty nozzle performance and reduced print quality. Ink and other fluids contain varying amounts of dissolved air. However, as ink temperature increases, the solubility of air in the ink decreases, which results in the formation of air bubbles in the ink. Higher drop ejection frequencies (i.e., firing frequencies) in printheads also cause an increase in the formation of air bubbles in the ink, in addition to causing increased temperatures. Therefore, the formation of unwanted air bubbles in ink delivery systems of inkjet printheads is an ongoing challenge as higher drop ejection frequencies are used to achieve increased printing speeds.